The invention relates to multi-element microphones, and more particularly microphones used in conjunction with digital signal processing for telematics applications.
Single-element microphones have been used for telematics speech-enabled applications. As an example, these microphones have been used in automotive hands-free cellular applications where good microphone performance is characterized by a combination of high speech recognition scores and high signal-to-vehicle-noise ratio under a variety of vehicle, road, and other noise conditions the driver is likely to encounter. In other words, the more the talker""s voice stands out from the background noise produced by the automotive environment itself, the better the performance of the microphone is considered. The target recognition rate for the industry for these telematics applications exceeds 99% under all conditions. Also, teleconferencing and installed sound applications may suffer from similar problems when single element microphones are used in environments that are associated with reverberation and ventilation noise.
In the automotive environment, a typically used microphone is a first order gradient, in which a single-element microphone is employed in a surface mount configuration designed to minimize pickup of vehicle noise and reverberation originating in a direction away from the talker. These microphones often have a bi-directional or cardioid polar response pattern. However, these microphones have a relatively wide maximum response window (corresponding to an acceptance angle), in which reflective surfaces on all sides of the passenger compartment, such as windows and leather upholstery, degrade performance and result in a low talker-to-vehicle-noise ratio when noisy driving conditions are encountered.
Alternatively, a dual-element microphone system in an array configuration may be employed in conjunction with digital signal processing to eliminate the undesired signal from the talker""s voice. Such a solution makes use of time-of-arrival information in identifying and amplifying a talker whose voice is received within an acceptance angle of a two-element array in order to reject noise from outside of the acceptance angle. With the array configuration, the talker""s voice may be isolated satisfactorily from undesired speech or speech-like noise (such as a passenger""s voice) in the horizontal plane. However, the system does not perform well with noise in the vertical plane, such as acoustical signals that emanate from audio speakers located in the vehicle. In addition, these systems require multiple microphone elements, as well as expensive hardware and software systems for performing the digital signal processing. A microphone arrangement coupled to a digital processor is typically expensive for automotive applications. Moreover, these systems have not demonstrated high speech recognition scores.
The approaches of the prior art, as described heretofore, provide acoustical systems having acoustical response characteristics that are not amenable for directive automotive acoustical applications. Thus, it would be an advancement in the art to provide method and apparatus that supports increased directivity and environmental rejection for a variety of applications including hands-free mobile phone use and telematics applications. Furthermore, it is desired that an acoustical system be cost effective, while having the capability of selectively processing distant acoustical sources.
The inventive method and apparatus overcome the problems of prior art by utilizing a plurality of port sub-arrays, in which each port sub-array comprises a plurality of acoustical ports. The ports of each port sub-array are spaced so that each port sub-array responds to acoustical signals generated by acoustical sources within an associated frequency range. In an embodiment of the invention, associated frequency ranges are related in a harmonic manner, in which each port sub-array corresponds to different frequency bands. The associated frequency range is a portion of the total frequency range of an acoustical system. Received acoustical signals from each of the port sub-arrays are coupled over acoustical pathways and are converted into electrical signals by capsules that may be mounted in a capsule mounting. The electrical signals may be filtered, such as to reduce spatial aliasing, and post processed to further enhance the frequency response of the array microphone.
In an embodiment of the invention, an acoustical system is configured to process acoustical signals within a desired horizontal angle and a vertical angle, while suppressing acoustical signals lying outside the angular ranges. The embodiment is configured such that voice recognition performance is enhanced. With a variation of embodiment, which may be applicable to automotive telematics, the port sub-arrays are mounted in a mirror casing so that a rear-view mirror may be tilted according to a talker""s line of sight through a rear window of an automobile, while providing desired directional acoustical characteristics for the talker. Variations of the embodiment support mounting the port sub-arrays in other locations of an automobile such as a steering wheel or instrument cluster. Other embodiments of the invention may process acoustical signals in different acoustical media, such as water, in order to support sonar applications. Further embodiments of the invention may process acoustical signals for controlling speech-enabled devices such as appliances.